Apparatus for stressing elongated members



APPARATUS FOR STRESSING ELONGATED MEMBERS Filed Oct. 18, 1965 2 Sheets-Sheet l lnvenlor GUNTER PERS ic/(E A Home y s Aug. 29, 1967 G. PERSICKE 3,338,553

APPARATUS FOR STRESSING ELONGATED MEMBERS Filed Oct. 18, 1965 2 Sheets-Sheet 1:

' Inventor G UNTER PERsic KE A ltorney;

United States Patent 3,338,553 APPARATUS FOR STRESSING ELONGATED MEMBERS Gunter Persicke, London, England, assignor to Christiani & Nielsen Limited, London, England, a corporation of Great Britain Filed Oct. 18, 1965, Ser. No. 496,980 Claims priority, application Great Britain, Nov. 12, 1964, 46,205/ 64 7 Claims. (Cl. 254-29) This invention relates to apparatus for stressing an elongated element and in particular to prcstressing a reinforcing element such as a steel cable, rod or wire prior to moulding a building constructional member, of concrete for example, around the element whereby the constructional member is made to incorporate the reinforcing element in tension.

In using such jacks for prestressing a reinforcing element for the aforesaid purpose, the element is disposed in a mould and at or near one end of the mould is anchored thereto with the other end of the element extending outside the mould. A jack is held against the outer end of the mould or a member connected thereto, and releasably fixed to the reinforcing element. The jack is then operated to exert a longitudinal pull on the element which is thereby extended. The known jacks used suffer from the disadvantages that they are incapable of imparting the necessary extension to an element by one throw of the jack, and that the jack used for the extension operation must remain in situ until the concrete has been poured into the mould and allowed to set.

The main object of the present invention is to provide a device in which the aforesaid disadvantages are minimised or eliminated.

According to the present invention an apparatus for 'tensioning an elongated element having one end anchored to' a rigid body and its other end provided withan abutment thereon, comprises a hollow elongated annular member for disposition around the elongated element, an elongated annular cylinder surrounding said annular member, a piston disposed within and in sliding engagement with said cylinder, sealing means between the piston and cylinder, the piston and cylinder being one connected to said hollow member and the other bearing against said abutment, and a pressure fluid inlet and outlet towards the head end of the cylinder, whereby when the apparatus has been assembled on the element between the abutment and the rigid body, admission of pressure fluid to the cylinder will cause relative movement between the piston and cylinder to extend the elongated element.

One preferred construction comprises an elongated annular cylinder having a longitudinal hollow core for disposition over the elongated element, an elongated annular piston rod around the core and longitudinally movable in the cylinder, an annular piston head connected to the inner end portion of the rod withinthe cylinder and having inner and outer annular hollow sealing rings to seal the head to the inner and outer walls of the interior of the cylinder, a pressure fluid inlet and outlet towards the head-end portion of the cylinder, whereby when the apparatus has been assembled on the element between an anchor on the free end of the element and an abutment fixed with respect to the rigid body admission of the pressure fluid to the cylinder will force the piston to move longitudinally of the cylinder to extend the elongated element.

. Preferably thehollow sealing rings surround inner and 3,338,553 Patented Aug. 29, 1967 outer circulation faces of the inner end portion of the piston and their hollow interiors open towat-ds the pressure fluid chamber in the cylinder and are covered by a plate having apertures through which the pressure fluid enters their interiors.

The end of the hollow core preferably enters a secondary annular cylinder having a second annular piston slidably disposed therein operable to ram an anchor between the elongated element and the rigid body when the elongated member has been tensioned and prior to removal of the apparatus from the elongated element.

The end of the cylinder remote from the piston head is closed by a cap having a central aperture therethrough to receive the piston rod, sealing means being provided between the cap and the piston rod to form a fluid-tight seal therebetween when pressure fluid is admitted to the cylinder at the cap end of the cylinder.

The piston rod may have a linear scale marked thereon moving past a datum point on the cylinder to indicate the length of extension imparted to the elongated element.

In order that the invention may be more fully understood an embodiment in accordance therewith will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a longitudinal cross section through a tensioning apparatus;

FIGURE 2 is a cross section on the line IIII of FIGURE 1 looking in the direction of the arrows; and

FIGURE 3 is a plan view of FIGURE 1.

In the drawings the same references are used to designate the same parts.

Referring to the drawings the apparatus comprises an elongated annular cylinder 1 having a longitudinal hollow core 2 for disposition over an elongated element to be tensioned (not shown). An elongated annular piston rod 3 is disposed around and in sliding engagement with the core 2 and is movable longitudinally in the cylinder 1, its upper end protruding from the top of the cylinder 1. Attached to the inner end portion 4 of the rod 3 within the cylinder 1 is the head 5 of an annular piston 6, the lower outer edges 7 of which are scale-d to the inner and outer walls 8 and 9 respectively of the interior of the cylinder by hollow sealing rings 10 and 11. The lower sealing rings 10 and 11 of the piston 6 are held in position by a plate 45 secured to the underside of the piston by screws 46. Holes 47 are provided in the plate opposite each of the lower sealing rings rings 10 and 11 so that when pressure fluid is applied to the underside of the piston '6, fluid will pass through the holes 47 into the hollow rings and cause the rings to flex outwardly against the walls 8 and 9 of the cylinder 1 to provide a fluidtight seal therewith. A similar effect is created by fluid entering any of the other sealing rings 10, 11, 30, 31. Pressure fluid inlets 12 and 13 are provided for the cylinder 1 and are shown more clearly in FIGURE -3.

The cylinder 1 has, on its lower end, an annular externally threaded projection or boss 14, onto which is screwed a hollow member 15. The hollow core 2 of the cylinder 1 extends into the member 15 to form a core 36 in a second annular cylinder 16 in which is slidably disposed a second annular piston 17, the outer edges of which are sealed to the inner and outer walls 18 and 19 respectively of the interior of the cylinder 16 'by hollow sealing rings 30 and 31. A pressure fluid inlet 32 is provided for the cylinder 16. Extending downwardly from the piston 17 is a short annular piston rod 20 which extends through the cylinder 16 and into a narrow bore 21 in the member 15 in which it is slidably disposed. The member 15 has an annular projection 22 extending from its lower end and adapted to receive a guide member 23 having a hollow portion 24 and an aperture 25 through its lower end 26. The guide member may be retained in position by suitable means such as one or more grub screws, one of which is shown at 27 so as to be quickly interchangeable with other guide members having end apertures of different sizes for the purpose to be described. A tubular element 28 is disposed in the hollow portion 24 of the guide member 23 with its lower end slidably engaged in the aperture 25 of said guide member 23. The element 28 has at its upper end a boss 29 of such a size as to be a sliding fit in the end of the annular piston rod 20, the lower end portion of the boss being formed as a flange 41 for engagemnt with the lower end of the piston rod 20'.

The outer wall of the upper end portion 50 of the cylinder 1 is threaded to receive a cap 51, having a bore 52 through its base 53 to allow passage therethrough of the piston rod 3-, said rod being in sliding engagement with the inner wall of the bore 52. The outer surface of the base 53 acts as a datum line whereby movement of the piston 6 in the cylinder 1 may be measured by reference to a scale marked on the outer wall of the piston rod. A further hollow sealing ring 54 is disposed in a recess adjacent to the bore 52 and forms a fluid-tight seal between the cap 51 and the piston rod 3 when the piston 6 is at the top of the cylinder 1 and fluid is admitted through the inlet 13 to move the piston 6 to the bottom of the cylinder.

In operation, an elongated element to be stressed (not shown), anchored to a rigid body, as for example a mould into which a concrete pile or the like is to be cast, below the lower end of the jack shown in FIGURE 1 is passed through the hollow centre of the apparatus formed by the cores 2 and 36 and tubular element 28 and anchored at its free end against the upper end 37 of the pitson rod 3 by a device 40 shown in dotted outline consisting of an annular boss 33 having tapered interior walls 34 and tapered segments 35 engaging round the element within the boss, the segments tightly clamping the element in the boss when an axial load is applied to the element in a direction towards the narrow end of the boss aperture.

Fluid pressure is then applied through the inlet 12- to the piston 6 which causes an axial load to be applied via the anchoring device 40 to the elongated element causing the latter to be extended by an amount equal to the distance moved by the piston 6, the maximum extension available being the full throw of the piston 6 in the cylinder 1 which may be in the region of seven inches.

When the desired extension has been imparted to the elongated element, fluid pressure is applied through the inlet 32 to the piston 17, causing it to engage the flange 41 of the tubular elemetn 28 to urge the lower end of the element 28 into engagement with an anchoring device (not shown), which may be similar to the device 40, to ram the anchoring device into position in the mould or the like to retain the stressed 'alongated element in stressed condition after removel of fluid pressure from the piston 6. When the anchor has been rammed home in this manner, the fluid pressure is released from the piston 17 and pressure fluid is admitted through the inlet 13 to the reverse side of the piston 6 to cause the latter to return to its original position in the cylinder 1. The anchor 40 may thereafter be removed and the apparatus withdrawn from the stressed elongated element.

It is possible to use the apparatus with elongated elements of different diameters, the guide member 23, tubular element 28 and cap 51 being interchangeable with similar components each having apertures just large enough to allow passage therethrough of the element to be stressed, to ensure that the latter is aligned substantially along the longitudinal axis of the apparatus.

In an alternative construction the piston 6 is fixed to the hollow member 2 and the cylinder abuts against the anchor 33 so that relative movement, under fluid pressure, between the cylinder and piston will extend the elongated element.

It will be seen that apparatus of the present invention enables a desired extension to be applied to an elongated element by a single movement of a jacking piston and provides a simple and eflicient means of ramming into position an anchor to retain the elongated element in stressed condition after removal of the apparatus therefrom.

I claim:

1. A jack, particularly for prestressing elongated reinforcing elements for concrete castings and adapted to cooperate with wedge gripping anchor means at both ends of said jack, comprising an outer body defining a cylindrical chamber, a tubular core extending substantially the full length within said chamber and having a cylindrical outer surface which jointly with said cylindrical chamber define an annular working cylinder, a transverse annular partition between and rigidly connecting said body and core, said partition being closer to one end of said body and core and subdividing said annular cylinder into major and minor cylinders, an annular piston within each said cylinder, an annular piston rod extending from each said piston in surrounding relation to the respective portion of said core and with the free end of each said rod cooperative with a wedge gripping anchor means, and pressure fluid passages through said body and respectively opening into each said cylinder, whereby the piston in said major cylinder is operative to actuate an anchor means and prestress a reinforcing element extending through said tubular core and the piston in said minor cylinder is operative to actuate another anchor means to hold the reinforcing element in its prestressed condition after retraction of the major cylinder piston and release of the anchor means actuated by its piston rod.

2. A jack according to claim 1 wherein the end of said rod opposite the piston in said major cylinder extends through the corresponding end of said body for engagement with an anchor means.

3. A jack according to claim 2 wherein said major cylinder piston rod has graduations on its outer surface and the outer surface of said body end constitutes a datum line cooperative with said graduations.

4. A jack according to claim 1 wherein said pressure fluid passages all open externally of said body adjacent said end through which said major cylinder piston rod extends.

5. A jack according to claim 4 wherein said body includes two portions, one of said portions defining said major cylinder and having said partition integral therewith and said tubular core is integral with said partition and has a portion projecting therefrom beyond said cylinder.

6. A jack according to claim 5 wherein said partition has an annular boss surrounding the projecting portion of said tubular core, and the other of said body portions comprises a hollow member secured on said boss and defining said minor cylinder, said hollow member having a bore axially aligned with said tubular core and concentric with said minor cylinder, the piston rod on the piston in said minor cylinder being slidably engaged in said bore.

7. A jack according to claim 6 comprising an annular flange extending from said hollow member, a guide member attached to said flange and defining a second concentric bore, a tubular element slidingly disposed within said second concentric bore, a cylindrical portion formed on the inner end of said tubular element and slidingly engaged in said annular piston rod, a flange on said tubular element engaging the free end of said rod so that axial 5 movement of said minor piston forces the tubular element through said guide member bore to engage an anchor and to ram the latter into its anchoring position to anchor the elongated element when in tension.

References Cited UNITED STATES PATENTS 1,945,151 1/1934 Marsh 92-482 X WILLIAM FELDMAN, Primary Examiner.

MILTON S. MEHR, Examiner. 

1. A JACK, PARTICULARLY FOR PRESTRESSING ELONGATED REINFORCING ELEMENTS FOR CONCRETE CASTINGS AND ADAPTED TO COOPERATE WITH WEDGE GRIPPING ANCHOR MEANS AT BOTH ENDS OF SAID JACK, COMPRISING AN OUTER BODY DEFINING A CYLINDRICAL CHAMBER, A TUBULAR CORE EXTENDING SUBSTANTIALLY THE FULL LENGTH WITHIN SAID CHAMBER AND HAVING A CYLINDRICAL OUTER SURFACE WHICH JOINTLY WITH SAID CYLINDRICAL CHAMBER DEFINE AN ANNULAR WORKING CYLINDER, A TRANSVERSE ANNULAR PARTITION BETWEEN AND RIGIDLY CONNECTING SAID BODY AND CORE, SAID PARTITION BEING CLOSER TO ONE END OF SAID BODY AND CORE AND SUBDIVIDING SAID ANNULAR CYLINDER INTO MAJOR AND MINOR CYLINDERS, AN ANNULAR CYLINDER INTO MAJOR CYLINDER, AN ANNULAR PISTON ROD EXTENDING FROM EACH SAID PISTON IN SURROUNDING RELATION TO THE RESPECTIVE PORTION OF SAID CORE AND WITH THE FREE END OF EACH SAID ROD COOPERATIVE WITH A WEDGE GRIPPING ANCHOR MEANS, AND PRESSURE FLUID PASSAGES THROUGH SAID BODY AND RESPECTIVELY OPENING INTO EACH SAID CYLINDER, WHEREBY THE PISTON IN SAID MAJOR CYLINDER IS OPERATIVE TO ACTUATE AN ANCHOR MEANS AND PRESTRESS A REINFORCING ELEMENT EXTENDING THROUGH SAID TUBULAR CORE AND THE PISTON IN SAID MINOR CYLINDER IS OPERATIVE TO ACTUATE ANOTHER ANCHOR TO HOLD THE REINFORCING ELEMENT IN ITS PRESTRESSED CONDITION AFTER RETRACTION OF THE MAJOR CYLINDER PISTON AND RELEASE OF THE ANCHOR MEANS ACTUATED BY ITS PISTON ROD. 